Relief printing plate having projections in non-image areas

ABSTRACT

A printing plate comprising a support, reliefs formed thereon as an image area, and from about 20 to about 4,000/cm 2  small projections thereon in non-image areas, the height of the reliefs being at least 0.05 mm larger than that of the small projections, and a method for making a printing plate which comprises: 
     A. superimposing a photosensitive resin layer having a thickness of at least 0.06 mm on a support, which is at least semi-transparent to actinic light, in intimate contact therewith; 
     B. exposing the resulting assembly to actinic light through an image-bearing transparency from the side of the photosensitive resin layer; 
     C. exposing the assembly to actinic light through a dot-image-bearing transparency having a transparent halftone dot area in a proportion of 1 to 40% from the side of the support to thereby form reliefs on the support, as image areas, and a number of small projections having a height of at least 0.01 mm and being lower than the height of reliefs, in non-image areas, wherein steps (b) and (c) may be conducted in the order: (b) and then (c); or (c) and then (b); or simultaneously.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a novel relief printing plate, and a methodfor making the same. More specifically, this invention relates to arelief printing plate in which staining of non-image areas duringprinting (usually called "bottoming") is prevented as a result ofproviding small projections in these areas, and to a method for makingthe same.

2. Description of the Prior Art

Various methods are in use for making relief printing plates, such asthe cast molding of type metal, the etching of a metal plate, or the useof a photopolymer. In all such methods, reliefs which form image areasare required to have considerable height. If reliefs are low in height,in relief printing ink cannot be prevented from adhering to non-imageareas and causes bottoming. In order to prevent bottoming, the reliefsare usually required to have a height of at least 0.5 mm.

When printing is carried out using a plate having such a relatively highrelief, especially on a rotary press, the printing plate must be mountedin cylindrical form on a plate cylinder. Hence, plates having such highreliefs (that is, thick plates) are inconvenient. For ease of mountingon a rotary press, flexible printing plates are also used. However, inorder to mount a printing plate on a plate cylinder, it is preferredthat the plate have as small a thickness as possible. Thinner platesalso have the advantage of lower costs of production. Furthermore,etching of a metal plate to provide low reliefs can be completed withinshort periods of time without problems such as side etching, and theetching process can be simplified. In the preparation of a reliefprinting plate using a photopolymer, on the other hand, that part of thephotopolymer layer which corresponds to the relief and which has athickness corresponding to the height of the relief must be photocured,as described in U.S. Pat. No. 2,760,863 (British Pat. No. 741,441,etc.). Accordingly, when the height of the relief is low, the thicknessof the photopolymer layer is small, and therefore, exposure time can beshortened.

Methods for printing with a plate having a relief height as low as about0.1 to 0.3 mm, known as "dry offset" printing, have recently beenregarded as promising. However, a printing press for printing with aprinting plate having a low relief height must have a fairly high degreeof precision to prevent ink staining of non-image areas, and care mustbe exercised in the maintenance of the same.

On the other hand, image areas of a lithographic printing plate used forconventional lithographic printing require no relief height. Even ifthere is some relief height, it is at most several microns, or the imageareas are lower in height than non-image areas. In lithographic printingplates, the non-image areas are rendered hydrophilic and water isretained in the non-image areas during printing to prevent the inkstaining of these areas. This naturally leads to problems duringprinting, and various restrictions are imposed on this type of printing.With a view to overcoming such difficulties, lithographic plates whichdo not use water have been suggested in which non-image areas are madeof an ink-repelling substance, such as a silicone resin, and such havecome into use to some extent. However, this technique still hasdisadvantages such as the need for using special ink.

In view of the state of the art, we performed extensive investigationsinto relief printing plates having relatively low reliefs with whichprinting can be performed on a conventional relief printing presswithout staining of non-image areas, which led to the present invention.

SUMMARY OF THE INVENTION

The printing plate of this invention is a novel printing platecharacterized by an image area consisting of reliefs with a height of atleast 0.05 mm and a non-image area having a number of small projectionswith a height of at least 0.01 mm, the height of the small projectionsbeing lower than that of the reliefs.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view of a printing plate formed inaccordance with the present invention.

FIG. 2 is a schematic representation of an exposure sequence utilizedfor forming a printing plate in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In the present specification the term "small projections" is used todescribe discontinuous protrusions in non-image areas which occurbetween the reliefs and which prevent bottoming. The small projectionsare not particularly limited as to shape, but generally have a heightgreater than their longest lateral dimension (with reference to thesupport), and most preferably, but not necessarily, exhibit a greaterlateral dimension at their contact point with the support than at theirtop. While the small protrusions need not necessarily be substantiallyperpendicular to the support and parallel to the reliefs, best resultsare only obtained when they are substantially perpendicular to thesupport and parallel to the reliefs, with their longest dimensionparallel to the reliefs. Most common shapes for the small projectionsinclude: conical, frustoconical, pyramidal, cylindrical, spherical,rectangular and hemispherical, though other polygonal and irregularshaped small protrusions can also be used.

FIG. 1 is a schematic sectional view of the printing plate of thisinvention. Reference numeral 1 represents the small projections; 2 thereliefs; and 3 a base plate. In the printing plate of this invention,the small projections present in the non-image area serve to preventbottoming. In the case of a relief printing plate with relatively lowreliefs which does not have such small projections, ink sits in thebottom areas between the reliefs, that is, in the non-image areas, andis transferred to a material being printed, thus causing bottoming(staining of non-image aras). In contrast, according to this invention,the presence of the small projections prevents ink staining of thenon-image areas, and even if ink stains the non-image areas, it is onlyprinted as minute dots and does not result in an appreciable degree ofbottoming.

As such a printing plate, there can also be used a printing plate whoseentire surface is a halftone image, with parts corresponding tonon-image areas of the original being highlight tones and the smallprojections being present as highlight dots. With such a printing plate,the height of the top of the small projections becomes equal to that ofthe reliefs as an image area, and at the time of printing, the smallprojections are clearly printed. Thus, the entire printed matter becomesdark, and the small projections are printed even in a non-image area ofsmall size. This results in a reduction of resolving power and poorreproducibility of fine design patterns. Furthermore, this printingplate suffers from the inconvenience of requiring halftone photographyfor all originals.

In lithographic printing plates used in conventional lithographicprinting, the surface of an aluminum or zinc plate as a base is grainedby mechanical, chemical or electrical means to roughen it. Therefore, inlithographic printing plates, that part of the base which corresponds tothe non-image area is roughened. The purpose of such graining, however,is to render coating of a photosensitive layer thereon easy, increasethe adhesion of images in image areas to the base plate, increase thehydrophilicity of the non-image areas, or to increase the retention ofdampening water. Thus, in the case of printing plates havingsubstantially no relief height, such as lithographic printing plates,even when the non-image areas are roughened, acceptance of ink to thesenon-image areas cannot be prevented unless dampening water is used.Furthermore, since the purpose of surface roughening is as mentionedabove, the degree of roughness is small (usually, about 1 micron orless), and small projections are not positively provided as in thepresent invention.

In contrast, the printing plate of the present invention ischaracterized by having image areas consisting of reliefs with a heightof at least 0.05 mm and non-image areas containing a plurality of smallprojections with a height of at least 0.01 mm, the height of the smallprojections being lower than that of the reliefs.

Since the printing plate of this invention contains reliefs with aheight of at least 0.05 mm, bottoming of non-image areas is prevented bythe action of the small projections provided therein without using thedampening water which is required in conventional lithography.

The height of the small projections in FIG. 1, that is, the distancefrom the surface of the base 3 on which the small projections 1 arepresent to the top of the small projections 4, must be at least 0.01 mm.If it is less than 0.01 mm, the effect of preventing bottoming isinsufficient. Furthermore, the small projections must be present inlarge numbers.

A suitable number of small projections capable of providing a sufficienteffect of preventing bottoming is at least about 20, preferably at least100, per square centimeter. The objects of this invention can beachieved when the number of the small projections is not more than about4,000 per square centimeter; when the number of small projections isincreased beyond this limit the bottoming preventing effect does notsignificantly increase while the preparation of such small projectionsbecomes difficult; accordingly, such is economically disadvantageous.There is no particular limitation on the shape or number of the reliefs.

It is not necessary that all of the small projections present have aheight of at least 0.01 mm; it is sufficient if the number of smallprojections which have a height of at least 0.01 mm is within the aboverange, and small projections of a height of less than 0.01 mm may bemixed with the higher small projections as described above. Since theyhave no beneficial effect, their presence can be ignored.

The top 4 of a small projection 1 gives a greater effect when it issmaller in area. Preferably, its area is not more than 0.04 mm². Theshape of the top may be any shape, such as circular or polygonal. Whenthe top is circular, the diameter is preferably not more than 0.25 mm,and when the top is polygonal, the length of the largest measurementdiagonal is preferably not more than 0.25 mm. As later explained, whenthe top area is essentially infinitely small, e.g., pyramid or truecone, the top area is represented by a lateral sectional plane taken 10microns below the actual top of the small projection.

The shapes of the small projections as a whole are not particularlyrestricted; they can be, for example, a cylinder, a cone, a pyramid, asphere, a hemisphere or an irregular granule. Preferably, they areconical or pyramidal in shape.

It is preferred that the tops of the small projections be as small inarea as possible, and their areas at the portion bonded to the baseplate be as large as possible so that they are not knocked off duringprinting. Accordingly, small projections of a conical or pyramidal shapeare most suitable.

With conical or pyramidal points, the area of the top could be madeessentially infinitely small. However, since adhesion of ink duringprinting occurs entirely in the vicinity of the top, the sectional areaof the small projections at a position 10 microns below their top ispreferably within the above-specified range. Usually, the top will beused for the area measurement, of course, but where the top is(essentially) a point (cone, triangle) this measurement is made 10microns down. Most preferably, the diameter or the length of the bottomat its largest measurement is at least about 1/5 the height of the smallprojections.

In order to secure a sufficient bottoming preventing effect at non-imageareas, it is preferred that the total sectional area of the tops of allof the small projections (measured at a distance 10 microns below thetop thereof for shapes such as cones, pyramids) should not be more than30% of the area of one side of the base plate 3; small projectionshaving a height of less than 0.01 mm are not included, of course.

The top 4 of a small projection is lower than the top 5 of the relief,and the distance between the top 4 and the top 5 is preferably at least0.05 mm. When the height of the small projections are substantially thesame as that of the reliefs, that is, when the distance between thepoint 4 and the point 5 is small, a halftone image in the image area andin the area of the small projections is printed, and sometimes, a moirepattern occurs.

The height of the relief of the printing plate in accordance with thisinvention must be at least 0.05 mm. There is no particular restrictionto the upper limit of the height of the relief, but since the purpose ofthis invention is to provide a printing plate having a relatively lowrelief height, it is sufficient for most printing processes if theheight of the relief is at most 0.5 mm.

Furthermore, as the relief height is preferably higher than that of thetop of the small projection by at least 0.05 mm, a preferred reliefheight is thus within the range of 0.06 to 0.5 mm.

Although the present invention gives printing plates having a relativelylow relief height, the plates may comprise reliefs with a height of morethan 0.5 mm when the bottoming of non-image areas cannot be preventedunless the relief height is higher, e.g., at least 0.5 mm (for example,in the case of printing paper boards, a relief height of more than 2 mmis required for printing).

A preferred method for making the printing plate of this inventioncomprises superimposing a layer of a photosensitive resin on a baseplate, which is transparent or semi-transparent to actinic light, inintimate contact therewith, exposing the assembly to actinic light fromthe side of the photosensitive resin layer through an image-bearingtransparency (such as a negative photographic film), and also exposingthe assembly to actinic light from the side of the transparent orsemi-transparent base (such as, e.g., a copying paper) base through adot-image-bearing transparency to form small projections in non-imageareas. The size of the small projections obviously varies depending uponthe distance of the dot-image-bearing transparency from thephotosensitive resin layer. Therefore, it is not preferred that thedistance between the base plate (support) and the dot-image-bearingtransparency be too great during exposure, and the distance ispreferably within 20 mm.

FIG. 2 ilustrates in schematic form the method of this invention. Aphotosensitive resin layer 6 is superimposed on a transparent orsemi-transparent member 3 in intimate contact therewith, and theresulting assembly is exposed to actinic light 7 through animage-bearing transparency 8 to cure portions 2' which correspond to thetransparent areas. On the other hand, actinic light is irradiated fromthe side of the transparent or semi-transparent member 3 through adot-image-bearing transparency 9 to cure portions 1' which correspond tothe small projections. While it is generally preferred that the smallprojections have a uniform numerical distribution in areas where theyoccur, this is not mandatory so long as a sufficient number of smallprojections are within the range heretofore set forth (at least about20/cm²).

The unexposed or uncured portions are washed away (developed) by anyconventional method used to form printing plates to provide the assemblyas illustrated in FIG. 1, in which cured portions 1' and 2' as shown inFIG. 2 are left as small projections 1 and relief areas 2 as shown inFIG. 2 are left on the transparent or semi-transparent member 3.

The photosensitive resin used in the present invention is a resin whichis cured upon exposure to actinic light, or which has reduced solubilityin a solvent as compared to its solubility before exposure to actiniclight. Such a photosensitive resin composition, for example, comprises acompound containing an addition-polymerizable unsaturated group as themain ingredient and a photopolymerization initiator. There are noparticular limitation on the properties of these components so long as aphotocurable composition of sufficient mechanical strength to be usefulis achieved, nor is there any special limitation in the molecular weightof the resulting photopolymer.

Examples of such compounds containing an addition-polymerizable groupare acrylic acid, methacrylic acid, esters of these acids, for example,alkyl, cycloalkyl, tetrahydrofurfuryl, allyl, glycidyl, or hydroxyalkylacrylates or methacrylates, mono- or di-acrylates and methacrylates ofalkylene glycols or polyoxyalkylene glycols, trimethylol propanetriacrylate and methacrylate and pentaerythritol tetraacrylate andmethacrylate; acrylamide, methacrylamide or their derivatives such asN-methylol acrylamide and methacrylamide, N,N'-alkylene bisacrylamidesand methacrylamides, and diacetone acrylamide and methacrylamide;addition-polymerizable unsaturated monomers such as styrene, vinyltoluene, divinyl benzene, diallyl phthalate, triallyl cyanurate, vinylacetate or acrylonitrile; unsaturated polyesters; alkyd resins; andunsaturated polyurethane resins such as polyurethane resins modifiedwith an addition-polymerizable unsaturated monomer having an activehydrogen such as a hydroxyalkyl acrylate or methacrylate.

Examples of photopolymerization initiators are benzoin, benzoin alkylesters, α-methylbenzoin and alkyl ethers, α-phenylbenzoin,α-allylbenzoin, anthraquinone, chloroanthraquinone, methylanthraquinone,ethylanthraquinone, benzil, diacetyl, acetophenone, ω-bromoacetophenone,α-naphthalenesulfonyl chloride, diphenyl disulfide, and dyes such aseosine or thionine.

The photosensitive resin composition comprises at least one compoundcontaining an addition-polymerizable unsaturated group and aphotopolymerization initiator, and, if desired, a heat polymerizationinhibitor to increase storage stability such as hydroquinone, p-methoxyphenol, catechol, tert-butyl hydroquinone, benzoquinone,p-phenylenediamine, picric acid, or phenothiazine.

Examples of such photosensitive resin compositions are disclosed in U.S.Pat. Nos. 2,760,863; 2,902,365; 2,927,023; 2,929,710; 2,972,540;2,997,391; 3,695,877; 3,677,920; and 3,858,510.

There can also be used a composition comprising a polymeric compoundwhich is soluble in water or an alkaline aqueous solution, such aspolyvinyl alcohol, polyvinyl alcohol derivatives, cellulose derivatives,polyacrylic acid, polyacrylamide or an alcohol-soluble polyamide, theaddition-polymerizable unsaturated compound and the photopolymerizationinitiator, and, if desired, a heat polymerization inhibitor, and thecomposition comprising a polyene, a polythiol and a photosensitizer asdisclosed in Japanese Pat. Publication No. 29525/71.

The polymeric compound mentioned above serves to increase the physicalproperties and the washing-out capability after photocuring and tosolidify the resin composition at room temperature prior to photocuring(since most of the unsaturated compounds are liquid at roomtemperature). It is preferably used in an amount of about 90 wt% or lessof the composition weight.

The photosensitive resin composition exemplified above is usually coatedin layer form on a support member which is transparent orsemi-transparent to actinic light in intimate contact therewith.

The support member which is transparent or semitransparent to actiniclight may, for example, be a plastic film or sheet, cellophane film,paper, glass sheet, glass cloth, or fabric. Plastic sheets areespecially preferred, e.g., films or sheets of plastics such aspolyethylene terephthalate, polycarbonate, polypropylene, polyvinylchloride, polystyrene, polyvinyl alcohol, polyacrylonitrile, polymethylmethacrylate, nylon, or acetyl cellulose. The support will generallyhave a thickness of 0.01 to 1 mm, more preferably 0.05 to 0.5 mm.

It is often effective to provide an adhesive layer on the side of thesupport member which makes contact with the photosensitive resin layerto increase adhesion in the final printing plate between these twolayers. Examples of suitable adhesives which can be used to form such anadhesive layer include polyurethane resins, epoxy resins, polyesterresins, melamine resins, urea resins, polyacrylates, natural rubbers orsynthetic rubbers such as polychloroprene rubber, nitrile rubber,styrene-butadiene rubber, butyl rubber and the like, polyvinyl acetate,polyvinyl chloride, polyvinyl butyral, cellulose acetate propionate andcellulose acetate butyrate as disclosed in U.S. Pat. No. 2,760,863. Thestructure disclosed in British Pat. No. 1,321,108 is exemplary of atransparent or semi-transparent support member having an adhesive layerformed thereon.

The image-bearing transparency is suitably a negative film with a silversalt image. There can also be used a material which is substantiallytransparent to actinic light, such as a plastic film or sheet, a glasssheet, a regenerated cellulose film or paper, on which a negative imageis formed by means such as printing, copying or transferring.

The dot-image-bearing transparency can be a halftone dot film preparedby uniformly exposing a photographic film through a contact screen orglass screen. A dry plate such as glass dry plate can also be usedinstead of the film.

The term "dot-image-bearing transparency" is used in a broad sense asthe dots can have any shape and the percentage area of the transparencyoccupied by the dots is relatively flexible. Most commonly, thedot-image-bearing transparency is a halftone dot screen (or screenedfilm, as such halftone dot screens are often termed in the art). Themost common form of a halftone dot screen comprises a plurality ofcrossing screen rulings which define the "dots" by the areastherebetween. Such are conventional in the art and will not be furtherdescribed at this point in the specification.

The screen ruling of the halftone dot film is not particularlyrestricted, but to obtain a preferred number of small projections it ispreferably 30 lines/inch to 150 lines/inch.

There can also be used a dot-image-transparency formed by providing dotimages on the above-mentioned substantially transparent material byvarious means such as printing, copying or transferring, and adot-image-bearing transparency prepared by forming dot images byperforating a film, sheet or metal plate which is non-transparent toactinic light.

In order to obtain suitable small projections, the area proportion ofthe transparent portion of the dot-image-bearing transparency which isto form small projections is preferably 1 to 40%. When the areaproportion is less than 1%, it is difficult to form small projections bythe method of this invention. When it exceeds 40%, it is difficult toobtain small projections suitable for sufficiently preventing thestaining of non-image areas.

According to the method of this invention, actinic light is irradiatedthrough the dot-image-bearing transparency to cure that portion of thephotosensitive resin layer which corresponds to the transparent portionsof the dot-image-bearing transparency to a height of at least 0.01 mm,and thus form small projections. The irradiated actinic light, afterfalling upon the photosensitive resin layer, decreases in intensity asit proceeds farther inside the resin layer. Accordingly, the curedportion becomes progressively smaller in area as the light advancesdeeper into the inside of the photosensitive resin layer. In otherwords, the small projections formed become tapered as they depart fromthe base plate, and in such form are preferred for use in thisinvention.

However, when the amount of exposure through the dot-image-bearingtransparency becomes very large, portions corresponding to the smallprojections are cured to a height corresponding to the thickness of thephotosensitive resin layer, whereafter curing in the transversedirection begins to increase the area of the small projections. Hence,the amount of exposure should be very carefully controlled. Also, inthis case the height of the small projections becomes equal to that ofthe relief, and the printing plates of this invention cannot beprepared.

Accordingly, the amount of exposure through the dot-image-bearingtransparency should be so adjusted that the height of the smallprojections is lower than that of relief image areas (the height of thereliefs being essentially equal to the height or thickness of thephotosensitive layer); in other words, the height should be adjusted sothat the exposed area is cured to a height lower than that correspondingto the thickness of the photosensitive resin layer. When the amount ofexposure is adjusted within such a range, the shape of the smallprojections becomes preferred as described above. Furthermore, asdescribed above, this adjustment is preferably effected so that theheight of the small projections becomes lower than that of the relief byat least 0.05 mm. As a general rule, the preferred exposure will bedetermined empirically by measuring the height of the small projectionafter a trial run until the desired exposure conditions are reached.

The side surfaces of the reliefs are preferably inclined so that therelief becomes progressively thicker as it approaches the base plate.However, since the curing of portions corresponding to the reliefs isperformed by irradiation through an image-bearing transparency from theside opposite the support, irradiation must be effected to a sufficientextent, which is contrary to the case of preparing the smallprojections; phrased differently, it is necessary to provide an amountof exposure sufficient to cure in relief areas sufficient to providereliefs with inclined surfaces, which can be approximated by exposingthe photosensitive resin layer as if it had a thickness greater than itsactual thickness. One means of providing an inclination to the sidesurfaces of the reliefs is by employing the method disclosed in U.S.Pat. No. 2,760,863 (corresponding to British Pat. No. 741,441) ineffecting irradiation at the time of relief preparation.

Irradiation of actinic light to cure relief portions as image areas andirradiation of actinic light to cure the small projections in non-imageareas should be correlated with each other. The amount of exposurevaries according to the intensity of the light source used, thephotocuring rate and thickness of the photosensitive resin and withother components of the printing plate, e.g., degree of transparency ofthe support of this invention. The amount of exposure required can,however, easily be determined by a few trial runs at, for example,varying exposure times. When the same light source is used for curingrelief portions and small projection portions, it is sufficient if theamount of exposure required to cure the small projection portions isless than one half that required to cure the relief portions.

During irradiation with actinic light, the image-bearing transparency,the photosensitive resin layer, the dot-image-bearing transparency andthe transparent or semi-transparent support are preferably in intimatecontact with each other to insure accurate reproduction of images. Whenthe photosensitive resin is liquid, or is a solid but with a tackysurface, the provision of an interlayer between the image-bearingtransparency and the photosensitive resin layer is advisable to protectthe image-bearing transparency or to prevent adhesion of theimage-bearing transparency to the photosensitive resin layer afterexposure.

As such as interlayer, a thin transparent pre-formed plastic film isgenerally used. Examples of such are polypropylene, polycarbonate,polyethylene terephthalate, acetyl cellulose, polyvinyl alcohol,cellophane film, and the like. The film preferably has a thickness of5 - 50 μ and can be peeled off after curing.

The objects of this invention can also be achieved by using thedot-image-bearing transparency as earlier described to simultaneouslyserve as the transparent or semi-transparent support. In this case, anadhesive layer as earlier described is preferably provided on that sideof the dot-image-bearing transparency with which the photosensitiveresin layer makes contact.

The sources of actinic light used for exposure in the present inventioncan be freely selected and include, for example, arc lamps, mercurylamps, xenon lamps, fluorescent lamps, ultraviolet light sources andsunlight, which contain radiation of a wavelength of 200 - 800 mμ,preferably 300 to 500 mμ.

After exposure to actinic light, the uncured portion of thephotosensitive resin layer is removed by a conventional method usingvarious solvents or solutions, for example, water, aqueous solutionssuch as alkaline aqueous solutions, e.g., solutions of NaOH, NaCO₃,NaHCO₃, borax, sodium phosphate, sodium silicate, triethanolamine, orthe like, or aqueous solutions of surface active agents, e.g., a soap,alkylbenzene sulfonates, alkylsulfonates, alkylamine chlorides,polyoxyalkylene glycols, polyoxyalkylene glycol alkylethers,polyoxyalkylene glycol alkylesters, sorbitan fatty acid esters,polyoxyalkylene glycol sorbitan acid esters, etc., and organic solventssuch as alcohols, e.g., methanol, ethanol, isopropanol, etc., acetone,benzene or trichloroethylene. If the photosensitive layer is liquidbefore exposure to actinic light, the unexposed portion(s) can also beremoved by vacuum suction, scattering by centrifugal force or by blowingcompressed air thereon.

In the method of this invention, exposure to actinic light through theimage-bearing transparency and exposure to actinic light through thedot-image-bearing transparency can be effected separately, in anydesired sequence, or simultaneously.

Before performing the exposure(s), the entire surface of the assemblycan, if desired, be exposed from the side of the transparent orsemi-transparent support member with the dot-image-bearing transparencyremoved. This pre-exposure procedure is effective for the formation ofreliefs and small projections if it is carried out to an extent whichdoes not cure the photosensitive resin layer, that is, to an extentwhich provides an excited state. When a preliminary exposure is usedwithin the range such that curing is not initiated, photopolymerizationcan immediately occur in a sequential step when additional exposure isapplied; this state is called the "excited state." Usually the exposureto provide the excited state is about 1/10 or less of that required forthe relief exposure.

Since the thickness of the photosensitive layer corresponds to therelief height, it is most preferably within the range of 0.06 to 0.5 mm.When reliefs having a larger height are required, the thickness of thephotosensitive layer may be larger than that specified above.

Since the photosensitive layer to be cured in the preparation of theprinting plate by the method of this invention can be thinner than thatin conventional photosensitive resin plates, the exposure time can beshortened and the accuracy of image reproduction can be increased.

Another method of preparing the printing plate of this inventioninvolves using a base or support having formed thereon small projectionsas described above as a support, superimposing a photosensitive resinlayer (as earlier described) on that surface of the support whichcontains the small projections in intimate contact therewith, and thensubjecting the assembly to conventional photosensitive resin platemanufacturing procedures as described, for example, in U.S. Pat. No.2,760,863. Duplicate plates may be prepared from the resulting plate asan original. Specifically, such a support having small projections isarranged in intimate contact with the photosensitive resin layer by, forexample, coating the photosensitive resin layer thereon, and actiniclight is irradiated onto the photosensitive resin layer through animage-bearing transparency (such as a negative photographic film) tocure exposed portions. Then, the uncured portions are washed away toform relief images on the support containing the small projections.

If desired, using the resulting printing plate as an original, duplicateprinting plates can be prepared by ordinary methods of duplicatingrelief printing plates, such as a stereo method, a rubber molding platemethod, a galvanoplate method, a duplicating method using athermoplastic resin, or the method involving the casting of a liquidphotosensitive composition as is disclosed in Japanese Pat. PublicationNo. 39244/73.

The photosensitive resin used in this alternative method is the same ashas been earlier described. The photosensitive resin composition issuperimposed in layer form, preferably at a thickness of 0.06 to 0.5 mm,on the support containing the small projections in intimate contacttherewith, and used in the preparation of printing plates by thealternative method of this invention.

As in the first-described embodiment of this invention, theimage-bearing transparency and the photosensitive resin layer arepreferably disposed in intimate contact with each other in view of theaccuracy of image reproduction. When the photosensitive resin is liquid,or is solid but has a tacky surface (a non-tacky solid is preferred),the provision of an interlayer as earlier described between theimage-bearing transparency and the photosensitive resin layer isdesirable to protect the image-bearing transparency or to preventadhesion of the image-bearing transparency to the photosensitive resinlayer after exposure.

After exposure to actinic light, the uncured portions of thephotosensitive resin layer can be removed by washing in the same manneras hereinbefore described.

The thickness of the photosensitive layer is prescribed so that theabove-mentioned relief height can be obtained, and is preferably 0.06 to0.5 mm.

The support used in the present invention is not restricted with respectto either material or thickness; usually, however, it is a film or sheetof a thickness of 0.01 to 1 mm, preferably 0.05 to 0.5 mm, made ofvarious plastics such as have been earlier described, metals such assteel, copper, aluminum, zinc, magnesium, etc., paper, glass, glasscloth, fabrics, etc. Transparent or nontransparent supports can be used,depending on the embodiment involved.

Various methods are available to prepare a support consisting of a baseplate with small projections thereon. For example, a photosensitiveresin layer having a thickness corresponding to the height of therequired small projections can be superimposed on a base plate inintimate contact therewith, and the resulting assembly subjected to aconventional platemaking method for photosensitive resin plates using ahalftone dot film as an image-bearing transparency. Alternatively, aresist such as a water-soluble bichromate colloid, polyvinyl cinnamate,etc., is coated on a metal plate, for example, a zinc plate, magnesiumplate, copper plate, etc., and in accordance with conventional methods,such as etching for the preparation of metal relief printing plates, ahalftone plate comprising less than 30 area % highlight tones is madefor use as the support. Further, a plastic sheet can be used as thesupport, and made into the support by embossing to form the smallprojections thereon. Furthermore, it is possible to bond a number ofminute granules, which meet the earlier recited limitations on the smallprojections, to the base plate to serve as the small projections.

Duplicate plates can be prepared from the abovedescribed printing platesas an original by various methods, for example, a paper matrix stereotype method which comprises making a paper matrix by a rolling press ora direct pressure process and then casting type metal thereon, forming arubber plate or plastic plate by forming a Bakelite matrix andhotpressing it using unvulcanized rubber or a thermoplastic resin as aplate-making material, or imparting electrical conductivity to a matrixprepared from the original, and electrodepositing copper, iron, ornickel, etc., thereon to form a galvanoplate.

As stated hereinabove, the method of this invention gives printingplates having relatively low relief images which can be used on ordinaryrelief printing presses without causing bottoming; no special printingpress is required.

The present invention has the advantage that the thickness of aphotosensitive layer as an image area can be smaller than in aconventional photosensitive resin plate. This is not only economicallyadvantageous, but also shortens the exposure time and improves theaccuracy of reproduction.

The following Examples are to illustrate the present invention withoutlimiting the same.

Unless otherwise indicated, all thicknesses are dry thicknesses.

Further, in all Examples there were more than 20 but less than 4,000small projections per square centimeter, and the number of smallprojections of a size less than 0.01 mm was negligible.

EXAMPLE 1

To 100 parts by weight of a polyester resin (acid value 35; molecularweight about 1,700) obtained by polycondensing propylene glycol,diethylene glycol, adipic acid, fumaric acid and isophthalic acid in amolar ratio of 0.30/0.20/0.15/0.25/0.10 were added 10 parts by weight of2-hydroxymethacrylate, 20 parts by weight of diethylene glycoldimethacrylate, 10 parts by weight of diacetone acrylamide, 1 part byweight of benzoin ethyl ether and 0.1 part by weight of p-methoxyphenol. These components were thoroughly mixed to form a photosensitiveresin composition.

A plate-making negative film for newspaper having a size correspondingto one page of a newspaper was placed on a horizontal glass plate, andcovered with a polypropylene film having a thickness of 20 microns. Thephotosensitive resin composition was then cast onto the polypropylenefilm using a doctor knife to a thickness of 0.2 mm. Onto the cast layerof the photosensitive resin composition there was then laminated a 100micro-thick polyethylene terephthalate film which had coated on onesurface with a polyurethane adhesive (a mixture of Nippolan 3002(trademark for a product of Nippon Polyurethane Kogyo; a polyesterpolyol) and Coronate L (polyisocyanate) at a weight ratio of 5:1) to adry thickness of about 10 microns so that the adhesive surface contactedthe photosensitive resin layer.

A halftone dot film having a transparent area proportion of 5% and ascreen ruling of 85 lines/inch was then placed on the polyethyleneterephthalate film. The assembly was exposed for 30 seconds from thenegative film side through the glass plate and for 5 seconds through thehalftone film to actinic light from a 3 kw water cooled super-highpressure mercury lamp placed 50 cm away from the assembly for bothexposures. The glass plate, negative film and polypropylene film werethen removed (stripped), and unexposed portions of the photosensitiveresin layer were washed with a 1% aqueous solution of borax to removethe same. The assembly was then dried, and re-exposed for 20 secondsusing the above lamp at 50 cm from above the reliefs and smallprojections to complete the cure. Thus, a printing plate for printingnewspapers was prepared. The height of the reliefs formed as image areasof this plate was 0.2 mm, and the height of each of the smallprojections in the non-image area was 0.05 mm. The shape of each of thesmall projections was that of a truncated cone with a diameter of about0.08 mm, on the average, at the adhesive surface on the polyester film.The small projections tapered towards their top, and the averagediameter at the top was about 0.02 mm. The shape of the reliefs, incross section, was semi-rectangular, i.e., there was a slight inwardtaper or shoulder from the bottom to the top, as is preferred in thepresent invention.

Printing was performed using the resulting plate on a newspaper rotarypress. Black small projections were slightly printed partly in thenon-image area of the printed matter, but such were insufficient to beconsidered bottoming.

For comparison, a printing plate having relief images with a height of0.2 mm was prepared in the same way as above except that the exposurefrom the halftone dot film was omitted. Printing was performed using theresulting plate in the same way. The printing was inferior as bottomingoccurred in most of the non-image areas except for a very small area.

EXAMPLE 2

The same polyurethane adhesive as was used in Example 1 was coated to athickness of about 5 microns on the surface of a halftone dot filmhaving a transparent area proportion of 5% and a screen ruling of 85lines/inch which had been made from a photographic film comprising a 100micron-thick polyethylene terephthalate film as a base.

The same procedure as in Example 1 was repeated except that thishalftone dot film replaced the polyethylene terephthalate film used inthe assembly of Example 1. A printing plate substantially identical tothat of Example 1 was obtained.

EXAMPLE 3

A mixture consisting of 90 parts by weight of polyvinyl alcohol (havinga saponification degree of 80% and an average degree of polymerizationof 500), 30 parts by weight of 2-hydroxyethyl acrylate, 30 parts byweight of triethylene glycol dimethacrylate, 1 part by weight of benzoinethyl ether, 0.1 part by weight of hydroquinone and 150 parts by weightof water was cast on a plate-making negative film (as was used inExample 1), which was carried on a glass plate and dried by hot air toform a layer of photosensitive resin composition having a thickness of0.20 mm.

The photosensitive layer was then bonded at its exposed surface to a 100micron-thick polyethylene terephthalate film via a thin layer of anadhesive composed of polyvinyl butyral.

The assembly was then exposed through the plate-making negative film viathe glass plate for 40 seconds to actinic light from 3kw water cooledsuper-high pressure mercury lamp 50 cm from the assembly.

A halftone dot film having a transparent area proportion of 3% and ascreen ruling of 85 lines/inch was superimposed on the surface of thepolyethylene terephthalate film of the above assembly, and the assemblywas exposed through the halftone dot film for 15 seconds using the samelight source and distance as above.

The unexposed portions were removed by washing with water at 40° C andthe assembly dried to prepare a printing plate. The height of thereliefs in the image areas was 0.20 mm, and the height of the smallprojections in the non-image areas was 0.04 mm.

The shape of each of the small projections and reliefs was substantiallythe same as in Example 1. The diameter of the small projections at theadhesive surface on the polyethylene terephthalate film was about 0.06mm on the average, and the diameter near the top was about 0.01 mm on anaverage.

Printing was performed using the resulting printing plate on a proofpress for relief printing. The resulting printing was good in qualitywithout staining of the non-image areas.

EXAMPLE 4

A plate-making negative film having a size corresponding to one page ofa newspaper (as in Example 1) was placed on a horizontal glass plate andcovered with a polypropylene film having a thickness of 20 microns. Thesame photosensitive composition as was used in Example 1 was cast ontothe polypropylene film to a layer thickness of 0.3 mm. Onto the castphotosensitive resin layer there was laminated a 100 micron thickpolyethylene terephthalate film coated on one surface with a 10 micronlayer of a polyethylene adhesive [a mixture of Nippolan 3002 (polyesterpolyol) and Coronate L (polyisocyanate) a product of Nippon PolyurethaneKogyo] at a weight ratio of 5:1, so that the adhesive surface of thepolyethylene terephthalate film contacted the photosensitive resinlayer.

Further, a halftone dot film having a transparent area proportion of 15%and a screen ruling of 85 lines/inch was placed on the polyethyleneterephthalate film, and the assembly then exposed for 45 seconds throughthe glass support and for 5 seconds from the halftone dot film sideusing a 3KW water cooled super-high pressure mercury lamp 50 cm from theassembly. The glass plate, negative film and the polypropylene film werethen removed, and the unexposed portions of the photosensitive layerwashed with a 1% aqueous solution of borax to remove the same. Theresulting product was dried and re-exposed from above the reliefs andsmall projections for 20 seconds at 50 cm. with the same light source aswas used above to complete the photocure.

A printing plate for printing newspapers was thus prepared. The heightof the relief as image areas of this plate was 0.3 mm, and the height ofeach of the small projections of the non-image areas was 0.07 mm. Eachof the small projections had a diameter of about 0.12 mm at the adhesivesurface and about 0.03 mm at the top of the cured photosensitive layer.The reliefs and small projections had shapes similar to those of Example1.

Printing was performed using this printing plate on a rotary press fornewspapers. The resulting printing was free from the staining ofnon-image areas.

For comparison, a printing plate having relief images with a height of0.3 mm was prepared in the same way as above, except that exposure fromthe halftone dot film was omitted. Using the resulting printing plate,printing was performed in the same way as above. Printing was very poorin quality with the occurrence of bottoming in substantial portions ofthe non-image area, only small areas being free of bottoming.

EXAMPLES 5 to 18

In each of the following runs, a printing plate with a relief height of0.4 mm as shown in Table 1 was prepared in the same way as in Example 1except that the photosensitive resin composition was spread to athickness of 0.4 mm using a doctor knife, the halftone dot films shownin Table 1 were used and exposure from the side of the halftone dot filmwas carried out for the exposure times shown in Table 1.

Printing was performed using each of the printing plates obtained.Except for the printing plate obtained in the Reference Example, theprinting obtained was good in quality without the staining of thenon-image areas. The printing obtained using the printing plate obtainedin the Reference Example contained black points all over the surface ofthe non-image areas, and moire occurred in the halftone dot portions ofthe image areas. The quality of the printing was deemed poor.

                                      Table 1                                     __________________________________________________________________________               Halftone-dot Film                                                                       Shape of the Small Projections                                           Area pro-                                                                     portion   Average                                                        Screen                                                                             of trans- diameter                                                                            Average                                             Exposure                                                                           ruling                                                                             parent    of the                                                                              diameter                                            time (lines/                                                                            portion                                                                            Height                                                                             bottom**                                                                            near the                                      Examples                                                                            (sec.)                                                                             inch)                                                                              (%)  (mm) (mm)  top (mm)                                      __________________________________________________________________________     5    5    45   10   0.13 0.22  0.06                                           6    5    65    5   0.05 0.10  0.03                                           7    5    65   10   0.08 0.14  0.04                                           8    5    65   20   0.12 0.20  0.05                                           9    5    100  10   0.05 0.09  0.02                                          10    5    100  15   0.07 0.11  0.03                                          11    5    100  25   0.09 0.14  0.04                                          12    5    120  10   0.06 0.08  0.02                                          13    5    120  20   0.07 0.10  0.04                                          14    10   45   10   0.18 0.25  0.07                                          15    10   65    5   0.12 0.12  0.05                                          16    10   65   10   0.16 0.15  0.06                                          17    10   85    5   0.09 0.03                                                18    10   85   15   0.13 0.13  0.03                                          Reference                                                                     Example                                                                             40   85   15   0.40 0.20  0.30                                          __________________________________________________________________________     *Shape was conical; average diameter near the top measured 10 μ below      the top                                                                       **The diameter at the surface bonded on the polyethylene terephthalate        film.                                                                    

EXAMPLE 19

Following the procedure of Example 1, the photosensitive resin wasentirely exposed for 0.5 second through the polyethylene terephthalatefilm prior to placing the halftone dot film on the polyethyleneterephthalate film to bring the same to the "excited state." Thehalftone dot film was then placed on the polyethylene terephthalate filmand the assembly exposed for 20 seconds through the glass plate and thenegative and for 3 seconds through the halftone dot film. The lamp anddistance used for all three exposures were the same as in Example 1, thetime of exposure being varied as indicated. The unexposed portions werewashed away as in Example 1. The resulting printing plate was the sameas obtained in Example 1.

EXAMPLE 20

Following the procedure of Example 4 except for varying as set forthbelow, the photosensitive resin was entirely exposed for 0.5 second asin Example 19 (pre-exposure to provide the excited state of thephotosensitive resin) through the polyethylene terephthalate film sideprior to placing the halftone dot film thereon and, of course, prior toexposure from the halftone dot film side and the negative film side. Theassembly was then exposed for 3 seconds from the halftone dot film sideand for 25 seconds from the negative film side using the lamp anddistance as in Example 4. The resulting printing plate was the same asobtained in Example 4.

EXAMPLE 21

The procedure of Example 1 was repeated except that each of a 0.1mm-thick cellulose triacetate, polycarbonate, polypropylene andpolyvinyl chloride film were used instead of the polyethyleneterephthalate film. The resulting printing plates were the same asobtained in Example 1.

EXAMPLE 22

A polyurethane adhesive (a mixture of Nippolan 3002 and Coronate L in aweight ratio of 5:1, supplied by Nippon Polyurethane Kogyo) was coatedto a thickness of about 5 microns on a 0.1 mm-thick polyethyleneterephthalate film. The same photosensitive resin composition as wasused in Example 1 was coated to a thickness of 0.05 mm on theadhesive-coated surface of the polyethylene terephthalate film, and thenthe photosensitive resin layer was covered with a polypropylene film ofthickness of 12 microns. A halftone dot film having a transparent ofarea proportion of 7% and a screen ruling of 65 lines/inch was placed onthe polypropylene film. The assembly was then exposed for 10 seconds toactinic light from a 3 KW high pressure mercury lamp placed 50 cm fromthe assembly. The halftone dot film and polypropylene film were thenremoved, and unexposed portions were washed with a 1% aqueous solutionof borax to remove the same, followed by drying to prepare a support.

The height of each conical small projection on the polyethyleneterephthalate film was 0.05 mm, and the diameter of each minute point 10μ below the top was 0.115 mm, which was substantially the same in sizeas the transparent portions of the halftone dot film. The area of thetop of the small projections was 0.01 mm², and the summation of all ofthe areas of the tops was 6.6% of the total support area of the sidecarrying the small projections.

The support was placed with the small projections facing upward and thesame photosensitive resin composition as was used in Example 1 was castonto the support to a thickness of 0.30 mm from the polyethyleneterephthalate film surface. The photosensitive resin layer was coveredwith the same polypropylene film as was used above, and a plate-makingnegative film having a size corresponding to one page of a newspaper asin Example 1 was superimposed on the polypropylene film. The assemblywas then exposed for 40 seconds through the negative film using the samehigh pressure mercury lamp as was used above. Unexposed portions werethen washed away as above, followed by drying and re-exposure for 20seconds from the same light source as above at the same conditions asabove. A printing plate was thus prepared.

Printing was performed using the resulting printing plate on a rotarypress for newspapers. The printing obtained was of good quality withoutbottoming in non-image areas.

EXAMPLE 23

A printing plate was prepared in the same way as in Example 22 exceptthat the thickness of the photosensitive resin layer at the time ofpreparing the relief images was changed to 0.20 mm, and the exposuretime was changed to 30 seconds. Printing was performed using theresulting printing plate on a rotary press for newspapers. Black smallprojections partly printed in the non-image areas, but they were not asconspicuous as bottoming. The printing obtained was of good quality. Thereliefs were 0.20 mm high and the small projections 0.05 mm high.

EXAMPLE 24

Using a halftone dot film having a transparent area proportion of 5% anda screen ruling of 85 lines/inch, a commercially available 0.84 mm-thickzinc PS relief plate (P.S. Fine Zinc, a product of Mitsui Kinzoku Kogyo)was subjected to baking and powderless etching in a conventional mannerfor the preparation of metal relief printing plates. There was obtaineda halftone printing plate, the entire surface of which was a highlighttone. The height of each of the hightlight dots in the half-tone platewas 0.15 mm. The highlight dots were conical and the section 10 μ belowthe top of each highlight dot was circular and had a diameter of 0.06 mmwhich, was smaller than the diameter of the dot of the halftone dot filmas an etching process was used.

The same photosensitive resin composition as was used in Example 1 wascast on the resulting halftone printing plate so that no bubbles werepresent in the layer among the highlight dots and the height of theresulting layer was 0.3 mm above the top of the highlight dots. Theresulting layer of photosensitive resin was then covered with apolyethylene terephthalate film having a thickness of 9 microns, and thesame negative film as was used in Example 1 was placed on thepolyethylene terephthalate film. The assembly was then exposed for 50seconds to actinic light from a 3 KW high pressure mercury lamp, andthen unexposed portions washed away, followed by drying and re-exposingas in Example 22 to form a printing plate having small projections innon-image areas. In this plate, the area of the top of each smallprojection was 0.0028 mm², and the summation of the areas of the topswas 3% of the total plate area bearing the small projections.

Printing was performed using the resulting printing plate on a plate bedpress for a letter press. The printing was of good quality withoutbottoming in non-image areas.

EXAMPLE 25

A mixture consisting of 90 parts by weight of polyvinyl alcohol(saponification degree 80%, average degree of polymerization 500), 30parts by weight of 2-hydroxyethyl acrylate, 30 parts by weight oftriethylene glycol dimethacrylate, 1 part by weight of benzoin ethylether, 0.1 part by weight of hydroquinone and 150 parts by weight ofwater was cast onto a horizontal glass plate and dried with hot air toform a sheet, about 0.45 mm thick, of the photosensitive resincomposition.

The resulting sheet was stripped from the glass plate and superimposedon the highlight dot surface of the halftone zinc plate produced inExample 24 and the assembly was subjected to lamination under pressurefor 2 minutes at 80° C. and 200 Kg/cm² to form a laminated plate havinga total thickness of 1.10 mm.

The same negative film as was used in Example 1 was placed on thephotosensitive resin layer of the resulting laminate and exposed for 60seconds to actinic light from a 3 KW high pressure mercury lamp placed50 cm from the laminate. The unexposed portions were removed by washingwith warm water at 40° C. to form a printing plate with smallprojections as in Example 24 and reliefs 0.40 mm high.

Printing was performed using the resulting printing plate on alithographic press. The printed matter obtained was of good quality freefrom the bottoming of the non-image area.

EXAMPLE 26

This example deals with the preparation of a matrix wherein plateshaving a topography which is the negative of those earlier formedresult.

Using a halftone dot film having a non-transparent area proportion ofabout 20% and a screen ruling of 65 lines/inch (the size of each dot inthe non-transparent portions was 0.20 mm), a PS zinc plate as was usedin Example 24 was subjected to baking and powderless etching in the sameway as in Example 24. A halftone plate with a uniform surface being ashadow tone was thus produced. Each of the dots in the resultinghalftone plate had a diameter of 0.25 mm on the surface of the plate anda depth of 0.11 mm. The shape of each dot was substantially conical, andthe diameter of the bottom portion was about 0.01 mm.

Using this halftone plate as a matrix, a polyvinyl chloride sheet 0.3 mmthick was pressure laminated thereon at 110° C and 100 kg/cm². About 650small projections each having a height of 0.11 mm and a top diameter ofabout 0.01 mm per cm² were formed on one surface of the polyvinylchloride sheet.

A printing plate was produced in the same way as in Example 22 exceptthat the resulting polyvinyl chloride sheet was used as a support.Printing was performed using the resulting printing plate, and theresults were as good as in Example 22.

EXAMPLE 27

The printing plate produced in Example 24 was heated to 70° C andexposed for about 2 minutes to actinic light from a 3 kw high pressuremercury lamp 30 cm away to strengthen the relief images.

Using the resulting printing plate as an original, a paper matrix wasmade by a rolling press, and a curved stereotype was produced by meansof a steroetype casting machine. The resulting stereotype was asubstantial duplicate of the type of printing plate obtained in Example24.

Printing was performed using the resulting stereotype on a newspaperrotary press. The printing was good in quality without appreciablebottoming in non-image areas.

COMPARATIVE EXAMPLE

In the preparation of the support in Example 22, the thickness of thephotosensitive resin layer was changed to 0.25 mm and the exposure timewas changed to 30 seconds. In the resulting support, the height of thesmall projections was 0.25 mm and the top of each small projection wascircular with a diameter of 0.115 mm.

A printing plate having small projections in the non-image areas of thesame height as that of the relief images was prepared as in Example 22,except that the thickness of the photosensitive resin layer on the smallprojection side of the support was 0.25 mm, and the exposure time waschanged to 35 seconds.

Printing was performed using the resulting printing plate on a newspaperrotary press. The small projections printed all over the non-imageareas, and although they were not quite bottoming, they were imprintedas a fine visual pattern. The printing thus had a poor resolving power,and the small projections and the dots formed moire patterns, leading topoor quality printing.

EXAMPLE 28

A support was prepared in the same way as in Example 22 except that ahalftone dot film having a transparent area proportion of 40% and ascreen ruling of 65 lines/inch was used. The top of each of the smallprojections in the resulting support was substantially square with eachside measuring 0.25 mm. The area of the top of the small projection was0.063 mm², and the summation of the areas of the tops was 41% of thetotal support area carrying the small projections.

Printing was performed using a printing plate prepared as in Example 22from the resulting support. In the resulting printing, small projectionsprinted all over the non-image areas except in the neighborhood of theimage areas while the printing was not of good quality, it was not quitebottoming.

EXAMPLE 29

A support was prepared in the same way as in Example 28 except for usinga halftone dot film having a transparent area proportion of 40% and ascreen ruling of 85 lines/inch. The top of each of the small projectionsin the support obtained was substantially circular with a diameter of0.21 mm. The area of the top of each small projection was 0.034 mm², andthe summation of the areas of the tops was 39% of the area of thesurface of the support carring the small projections. The reliefs andsmall projections were otherwise the same as in Example 28.

Printing was performed using a printing plate prepared from theresulting support as in Example 1. In the resulting printing, smallprojections were printed in non-image areas, and the printing was not ofgood quality; however, bottoming of the non-image areas was notpronounced.

EXAMPLE 30

The same procedure as in Example 1 was repeated except that a 0.20 mmthick polyvinyl chloride film was used instead of the polyethyleneterephthalate film coated with the polyurethane adhesive. The resultingprinting plate was substantially the same as obtained in Example 1.

EXAMPLE 31

The same procedure as in Example 1 was repeated except that instead ofthe polyethylene terephthalate film coated with the polyurethaneadhesive a 0.10 mm thick polypropylene film (one surface of which hadbeen corona discharge treated) was used, and such was laminated so thatthe treated surface contacted the photosensitive resin layer. Theresulting printing plate was substantially the same as in Example 1.

EXAMPLE 32

To 200 parts by weight of polyethylene adipate diol (molecular weight2,000) were added 34.8 parts by weight of tolylene diisocyanate and 0.5part by weight of dibutyl tin laurate, and the mixture was heated at 70°C for 2 hours to form polyethylene adipate containing terminalisocyanate groups. The resulting product was reacted with 100 parts byweight of an ethylene oxide/propylene oxide copolymer(block-copolymerized diol containing 35% by weight of ethylene oxide;molecular weight of 2,000) to form a block copolymer containing terminalisocyanate groups. To 300 parts by weight of the block copolymer wereadded 25 parts by weight of 2-hydroxyethyl methacrylate and 0.1 part byweight of hydroquinone, and the mixture was heated at 70° C for 2 hoursto form a polymer.

300 Parts by weight of the resulting polymer were mixed with 75 parts byweight of 2-hydroxyethyl methacrylate, 15 parts by weight of2-ethylhexyl acrylate, 30 parts by weight of n-butyl acrylate and 6parts by weight of benzoin ethyl ether to form a photosensitive resincomposition.

The resulting composition was coated to a thickness of 0.4 mm on apolypropylene film covering a negative film in the same manner as inExample 1. Then, a polyethylene terephthalate film was laminated ontothe photosensitive resin layer obtained. A dry glass plate on which hadbeen photographed half-tone dots (65 lines/inch with a transparent areaproportion of 10%) was placed on the polyethylene terephthalate film,and actinic light was irradiated thereon for 8 seconds through the dryglass plate from a 3 KW high pressure mercury lamp 50 cm from theassembly. The assembly was then exposed for 60 seconds from the negativefilm side using the lamp and distance described above.

Unexposed portions were removed by washing with 2% aqueous solution of asodium alkyl (C₁₂) benzenesulfonate, followed by drying to form aprinting plate.

The height of the relief image areas of the resulting printing plate was0.4 mm, and the height of the small projections in the non-image areaswas 0.12 mm (average). The shape of the small projections was nearlyconical, and they had a diameter of about 0.03 mm 10 μ below their top.Other dimersion were substantially similar to Example 28.

Printing was performed using the resulting printing plate on aflexographic press. The resulting printing was of good quality withoutbottoming in the non-image areas.

On the other hand, when a printing plate was produced in the same way asabove except that the exposure from the side of the dry glass plate wasomitted, and printing was performed using the resulting printing plate,the printing was of poor quality with substantial bottoming in non-imageareas.

EXAMPLE 33

A 0.6 mm-thick polypropylene sheet was superimposed on a paper matrixprepared as in Example 27, and the assembly was hot-pressed at 110° Cand 50 kg/cm² to prepare a printing plate composed of polypropylene. Theresulting printing plate had a total thickness of 0.55 mm, and the samesmall projections as in Example 24 were formed in the non-image areas.The relief height of the image area was 0.3 mm larger than the height ofthe small projections.

Printing was performed using the resulting printing plate. The resultsas in Example 24.

While the invention has been described in detail and with reference tospecific embodiments thereof, it will be apparent to one skilled in theart that various changes and modifications can be made therein withoutdeparting from the spirit and scope thereof.

What is claimed is:
 1. A printing plate comprising a support, reliefscomprising photocured photosensitive resin formed thereon as an imagearea and from about 20 to about 4,000/cm² small projections thereon innon-image areas, the height of the reliefs being at least 0.05 mm largerthan that of the small projections, the top of each small projectionhaving an area of not more than 0.04 mm², and the summation of the areasof the tops of the small projections being not more than 30% of the areaof the support, the diameter of the top surface of each of the smallprojections being not more than 0.25 mm and the diagonal length of thetop surface of each of the small projections being not more than 0.25mm.
 2. The printing plate of claim 1 wherein the reliefs and smallprojections on the support comprise a photocured photosensitive resin.3. The printing plate of claim 1 wherein the support has a thickness of0.01 to 1.0 mm.
 4. The printing plate of claim 1 wherein the height ofthe reliefs is 0.05 to 0.5 mm.
 5. The printing plate of claim 1 whereinthe support is a member selected group consisting of transparentplastics films and sheets and semi-transparent films and sheets having athickness of 0.01 to 1.0 mm.
 6. The printing plate of claim 5 whereinthe support is provided with an adhesive layer thereon.
 7. A printingplate duplicated from the printing plate of claim 1 as an original.